1. Field of the Invention
This invention relates to an ink jet recording apparatus, and more particularly, it relates to an ink jet recording apparatus having a mechanism for detecting an amount of ink in an ink tank in which ink is stored.
2. Related Background Art
First of all, a conventional ink jet recording head of a kind having an ink tank used as an exhaust ink tank will be explained. In the conventional ink jet recording apparatus of this kind, ink discharging openings of recording heads would be clogged or jammed due to increase of viscosity of ink in the unused or rarely used recording head or heads and/or adhesion of dust in the discharge openings of the head. In order to remove such viscous ink and the like from the recording heads, various head restoring mechanisms have been used. For example, such head restoring mechanisms comprise means for discharging the viscous ink from the related discharge opening of the recording head by pressurizing the ink in the head or means for removing the viscous ink from the related discharge opening by sucking the ink through the medium of a cap for covering the discharge openings to protect them. The exhaust ink including the removed viscous ink was reserved in a predetermined exhaust ink tank.
FIG. 1 shows an example of the conventional ink jet recording apparatus having such head restoring mechanism, as a perspective view.
In FIG. 1, a waste or exhaust ink tank 1 formed integrally with ink cartridges 2 for containing colored ink such as cyan ink, magenta ink, yellow ink and black ink, respectively is mounted in a carriage 3. A recording head 5 and a printed circuit board 6 are also mounted on the carriage 3.
The carriage 3 can be shifted along two slide shafts 8 by a driving force transmitted to the carriage through a driving belt 9. As the carriage 3 is shifted, the recording head 5 records or prints images on a recording sheet as a recording medium fed onto a platen 7 by discharging ink on a surface of the recording sheet. During the recording operation, the carriage 3 is shifted appropriately or at a predetermined timed relation up to a position where the recording head 5 faces a cap 11. In this position, a head restoring (discharge restoring) operation is performed by means of a discharge restoring apparatus 10.
In the discharge restoring operation, the whole discharge restoring apparatus 12 and a waste ink pipe 12 are protruded into a path of the recording head 5 so that the recording head 5 is capped or covered by the cap 11 (i.e., the discharge openings of the head is covered) and the waste ink pipe 12 is connected to a predetermined portion of the waste ink tank 1. Then, the ink is sucked from the recording head 5 by a pump (described below) arranged in the discharge restoring apparatus 10 and is collected in the waste ink tank 1 through the waste ink pipe 12.
FIG. 2 shows details of the discharge restoring system. The four recording heads 5 corresponding to cyan ink, magenta ink, yellow ink and black ink, respectively are capped or covered by the four corresponding caps 11. The waste ink sucked from the four recording heads 5 by means of a suction pump 101 is combined as a single stream and is sent to the waste ink tank 1 through the waste ink pipe 12.
In this connection, when the waste ink tank is filled with a predetermined amount of ink, such waste ink tank must be replaced by a new empty one; otherwise, if the waste ink is continued to be sent to the filled waste ink tank, the ink will overflow out of the ink tank, thereby smearing or contaminating the electric systems such as the printed circuit board and the like to damage them.
For this reason, various techniques for detecting a predetermined amount of ink collected in the waste ink tank have been proposed.
As an example of such detecting technique having the simplest construction, the waste ink tank was made of transparent material. In this case, the amount of the waste ink collected in the ink tank could be visually checked, thus preventing the overflow of the ink by appropriately replacing the waste ink tank by a new one.
Another technique was to indicate the predetermined amount of ink by detecting the weight of the whole waste ink tank including the waste ink therein. For example, a pair of scales (seesaw type) on one of which the waste ink tank mounted was used. In this case, when the amount of ink in the waste ink tank exceeded a predetermined level, the ink tank was lowered, which condition was detected electrically or physically.
According to another detecting technique, an ink absorbing material which increases its volume by absorbing the ink therein was disposed in the waste ink tank. With this construction, as the waste ink was collected in the waste ink tank, the ink absorbing material swelled or expanded in the ink tank gradually to finally occupy the greater part of the volume of the ink tank, which condition was detected electrically or optically.
However, in the above-mentioned visual detection (use of the transparent material), while the construction is simple, an operator must always monitor or check the amount of ink in the ink tank, and thus, it is extremely inconvenient for the operator who engage the printing operation.
Further, in the above-mentioned weighting detection (use of the seesaw), large space is required to install such weighting detection system, which is contrary to compactness of the ink jet recording apparatus. Further, sensors for detecting the weight of the whole waste ink tank is expensive, making the whole ink jet recording apparatus expensive.
Further, in the above-mentioned use of the ink absorbing material, such ink absorbing material is relatively expensive, and since the ink absorbing material does not necessarily expand uniformly, incorrect detection will occur.